1. Field of the Invention
The present invention relates to high-pressure, plunger-type liquid pumps adapted for continuous operation at pressures at or above about 15,000 psi., and to an improved, long-life flow control valve for regulating the flow of liquid into and out of the plunger cylinder of a high-pressure, plunger-type liquid pump.
2. Description of the Related Art
Positive displacement, high-pressure liquid pumps have been in use for some time. However, it has been found that commercially available pumps fail rapidly when operated continuously at liquid pressures exceeding about 8,000 psi. and at flow rates of about 10 gpm. per plunger (47 hydraulic horsepower equivalent). In order to increase the relatively short operating time between failures for such liquid pumps the pressures and flow rates at which the pumps can be effectively operated must be limited, which thereby limits the number and types of applications for such pumps.
Investigation has revealed that failures of the preexisting high-pressure pumps and valves was often caused by a cross-port structural arrangement, wherein, when the high-pressure liquid underwent abrupt changes in flow direction and pressure, and transferred this pressure change to the pump housing the result was erosion and stress cracking of the metal at the port areas of the valve and pump housing or casing. Accordingly, the pumps and valves when operated at high pressures, especially pressures of over about 10,000 psi., would be required to be removed from service and repaired on a frequent basis, and consequently the use of the pumps at such high pressures resulted in very high maintenance costs per pump operating hour.
One form of pump and valve structure that was devised in an effort to improve the operating life of high-pressure pumps at high-pressure conditions is disclosed in U.S. Pat. No. 4,878,875, which issued on Nov. 7, 1989 to J. Edward Stachowiak. That patent identifies some of the earlier-issued patents that disclose the right angle, or cross-port bore arrangements in the prior art pumps, and it also identifies patents that have valve bores that are arranged coaxially with the pump plunger bore access.
The above-identified Stachowiak patent discloses a pump structure that includes a liquid manifold, or "fluid end," as it is referred to in the art, that receives a cartridge-type valve that is carried within the manifold and is positioned coaxially with the pump plunger axis. The valve is readily replaceable, but only upon separation of the liquid manifold from the pump housing. Additionally, the disclosed valve also seats on the outermost surface of a stuffing box that defines the pump plunger chamber. Removal of the cartridge valve requires removal of the manifold block from the pump drive housing. The manifold block is pivotally carried by a flange plate that is secured to the pump drive housing structure, and it surrounds a removable stuffing box that includes the pump plunger. Furthermore, the Stachowiak cartridge valve, although an improvement for high-pressure pumps having relatively low liquid output rates, cannot effectively be scaled up to higher liquid output rates of beyond about 50 hydraulic horsepower per cylinder because the valve structure includes a relatively large diameter discharge valve, which upon scaling up to higher output rates results in a larger valve cavity diameter that would be subjected to stresses that exceed the strength of the steel available for the manufacture of fluid ends for such pumps. Therefore, the Stachowiak valve and pump design, although an improvement over the previously-existing valve and pump designs, has limited applicability because of the limitations caused by the structural configuration of the cartridge valve.
It is an object of the present invention to overcome the shortcomings of the prior art pump and valve structures for use in high-pressure liquid pumps.
It is a further object of the present invention to provide a high-pressure pump design that is easily maintainable and that provides rapid accessibility to the flow control valves for servicing.
It is another object of the present invention to provide an improved high-pressure liquid pump structure in which the high-pressure plunger cylinder and the liquid distribution manifold are housed in a unitary structure, within which the flow control valve is also positioned.
It is a still further object of the present invention to provide a liquid manifold for a high-pressure liquid pump in which access to the liquid flow control valves can be had without removing the liquid manifold from the pump housing.
It is still another object of the present invention to provide a pre-assembled cartridge-type valve that can be readily installed and removed from the pumping cylinder of a high-pressure liquid pump for rapid servicing.
It is another object of the present invention to provide a pre-assembled cartridge type valve in which all moving parts are internal to the valve.
It is another object of the present invention to provide a pre-assembled cartridge type valve in which the outside of the valve housing contains the required drilling and plenum chambers leaving the bore(s) in the pump housing essentially free of abrupt diametrical changes which can be a source of stress concentration and failures.
It is still another object of the present invention to provide a pre-assembled cartridge type valve in which the principal stresses are contained within the cartridge, a replaceable and repairable item, and not transferred to the valve housing, a much larger and generally unrepairable item.
It is another object of the present invention to provide a high-pressure liquid flow control cartridge valve that has a relatively loose fit in a liquid manifold and that includes simple seals and requires no close tolerance, metal-to-metal contact.